Vesicular materials and the use of such to produce photographic reproductions



VESICULAR MATERIALS AND THE USE OF SUCH pp ignonucn PHOTOGRAPHIC REPRODUC- Rienzi B. Parker, 129 Cherry Brooke Road, Weston,

Mass., and Brian V. Mokler, 66 Dana St., (Iambridge,

Mass. N0 Drawing. Filed July 31, 1964, Ser. No. 386,755 8 Claims. (Cl. 96-49) V a diazo compound, dispersed throughout the coating.

When the film is exposed to light, the sensitizer releases molecules of a gas-nitrogen in the case of diazo compounds. These do not form vesicles immediately, but they do so when the film is heated, presumably because .the vehicle is relaxed sufliciently on heating for the gas molecules to form bubbles and for the bubbles to expand. The resulting vesicles make the vehicle opaque to transmission of light in the exposed areas and also reflect and scatter light so that they appear white.

The early vesicular materials employed gelatin as the I vehicle. These suffered from the difliculty that the vesicular images obtained faded rapidly. Later work has revealed that this problem was caused, in part, by the sensitivity of gelatin to water. Gelatin vehicles absorbed moisture from the atmosphere and became soft, thus collapsing the vesicles and destroying the image.

An improvement in vesicular photography which avoided this difficulty is described in US. Patent 3,032,414. In that improvement, a vehicle is prepared from certain non-hygroscopic resin materials which are combined with a sensitizer in an organic solvent for the components. A uniform water-free mixture of the components is formed in the solvent and this can be applied to the backing to form the vehicle.

Non-hygroscopic resin materials which are described therein as satisfactory were synthetic, water-insoluble, non-hygroscopic, non-water swelling, highly linear thermoplastic resins selected from the group consisting of homopolymers of styrene, homopolymers of vinyl chloride, homopolymers of vinylidene chloride, copolymers of vinyl chloride with a different vinyl monomer and copolymers of vinylidene chloride with a vinyl monomer. The vehicles were found to require a permeability constant for nitrogen within the range of 8.6 10 to 8 10 to avoid escape of the gas before development and nevertheless permit diffusion of the gas to form vesicles during the development. The preperation of the vehicle must also avoid unduly high temperatures and other conditions which lead to the decomposition of the 3,251,690 Patented May 17, 1966 "Ice rigid under the conditions to which it is exposed, such as heat and moisture. Resistance is achieved in the improved materials described in the aforesaid Patent 3,032,414, and in the present invention further unexpected improvements in heat resistance are obtained.

Accordingly, it is an object of the present invention to provide an improved vesicular record material which can be developed to produce an image stable atvery high temperatures. This and other objects are achieved by employing as a vehicle acopolymer of acrylonitrile with a lower alkyl acrylate or methacrylate in which the alkyl group has from 1 to about 8 carbon atoms and in which the amount of acrylonitrile is between 45 and molar 7 percent. Of the alkyl acrylates and methacrylates, those containing 1 to 4 carbon atoms are preferred. Suitable acrylates are the methyl, ethyl and butyl esters. Suitable methacrylates include the methyl, ethyl, propyl and butyl esters. Preferred copolymers are those of acrylonitrile with an alkyl acrylate containing 65 to 85 percent acrylonitrile and of these, the copolymers containing 15 to 35 percent ethyl acrylate are regarded as particularly useful. with a sensitizer and a coating is prepared on a suitable backing. The resulting film is exposed to light and developed by heating briefly to an elevated temperature, to produce a photograph which is stable at temperatures as high as 200 F.

The polymer used may be prepared by conventional polymerization techniques. Solution polymerization has been found particularly suitable and is illustrated in the following examples.

Example I Ethyl acrylate and acrylonitrile were first purified by distilling the acrylonitrile at reduced pressure and by washing the ethyl acrylate with an aqueous solution of sodium hydroxide. A three-necked flask equipped with a thermometer, a stirrer and a nitrogen bubbler and reflux condenser was used as the polymerization vessel. The vessel was charged with 225 ml. tertiary butyl alcohol as a solvent, 0.451 gram benzoyl peroxide, 26.2 grams of acrylonitrile and 25.0 grams of ethyl acrylate. Nitrogen was bubbled through the mixture, which was stirred thoroughly at a rate somewhat greater than 5 cc. per minute. The reaction mixture was heated from its initial temperature of approximately 15 up to 60 during the space of one-half hour while the stirring continued. It was then held at a temperature of 60-65? C. for an additional two hours. At the end of this time the contents ofthe flask were poured into one liter of well-stirred V methanol. A portion of the product was scraped from the walls of the flask and added to the methanol. The product was filtered from the methanol and, after rinsing with additional methanol, it was placed in an oven at F. (70 C.) for 18 hours to remove the solvents. The yield was approximately 17 grams of a copolymer having a composition of about 75 molar percent acrylonitrile and 25 molar percent ethyl acrylate.

The copolymer composition of 45-90 mole percent acrylonitrile and 10-55 mole percent acrylate is the composition of the copolymer itself and these proportions may be different from those of the monomers used in the polymerization because of differences in the rate at which the respective monomers enter into the polymerization. When this is the case, polymerization should not be continued long enough for there to be a large change in the relative amounts of monomers or the monomer which is consumed more rapidly should be replenished during the reaction in accordance with conventional polymerization techniques.

The copolymer is dissolved in a solvent together 3 Example II Methyl methacrylate and acrylonitrile monomers were first freed of inhibitors by treatment with silica gel. A three-necked flask equipped with a thermometer, a stirrer, and a nitrogen bubbler and reflux condenser was used as the polymerization vessel. ,The vessel was charged with 250 ml. tertiary butyl alcohol as a solvent, 0.463

gram benzoyl peroxide, 29.6 grams acrylonitrile, and 6.2 grams methyl methacrylate. Nitrogen was bubbled through the constantly stirred mixture at a rate somewhat greater than cc. per minute. The reaction mixture was heated from its originaltemperature of 22 C. to 65 C. in 4-hour as stirring continued. It was then held at 65-68 for an additional 1% hours. Atthe end of the reaction period, the contents of the flask were poured into one liter of well-stirred methanol. The product was recovered from the methanol by filtration and, after additional washing and rinsing, allowed to dry overnight at room temperature. The yield was approximately 2.1 grams of copolymer which contains approximately 76 mole percent acrylonitrile and 24 mole percent methyl methacrylate.

If the copolymerization reaction is allowed to continue for too long a period, an unsuitable material is obtained. Thus, if the above preparation is allowed to continue reacting until approximately 40' weight percent of the monomers has been converted to copolymer, the product obtained is insoluble in solvents preferred in the preparation of vesicular coatings. Either low conversion polymerizations or the periodic replenishment of methyl methacrylate in the polymerization mixture are techniques suitable for controlling the product composition. A copolymer composition of 65-85 mole percent acrylonitrile and 35-15 mole percent methyl methacrylate appears to be preferable to obtain the desired combination of properties, these proportions having the amounts of monomers actually incorporated in the polymer.

The sensitizer must be capable of dispersion within the vehicle for the purpose of the required definition as described in the aforesaid U.S. patent.

Among the sensitizers, those which liberate nitrogen units upon irradiation such as para-diazo dimethyl aniline zinc chloride are especially valuable although other compounds for example of the type which liberates carbon oxides can be used. The following substances are illustrative of those which are useful:

p-Diazo diphenylamine sulfate,

p-Diazo diethylaniline zinc chloride,

p-Diazo ethyl hydroxyethylaniline zinc chloride,

p-Diazo ethyl methyl aniline zinc chloride,

p-Diazo diethyl methyl aniline zinc chloride,

p-Diazo ethyl hydroxyethylaniline zinc chloride,

1-diazo-Z-oxynapthalene-4-sulfonate,

p-Diethylaminobenzenediazonium chloride ZnCl 4-benzoylarnino-2-5-diethoxybenezene diazonium chloride,

the p-chlorobenzene-sulfonate of 4-diazo-l-cyclohexylaniline,

the p-chlorobenzene-sulfonate of 4-di'azo-2-methoxy-lcyclohexylaminobenzene,

' the tin chloride double salt of 4-N-methylcyclohexylaminobenzene diazonium chloride, p-Acetaminobenzene diazonium chloride, 4-dimethylaminobenzene diazonium chloride, 3-methyl-4-diethylaminobenzene diazonium chloride, 4-morpholino-benzene diazonium chloride, 4-piperidyl-2,5-diethoxy-benzene diazonium chloride, 1-dimethylaminonapthalene-4-diazonium chloride, 4-phenylaminodiazobenzene diazonium chloride.

The support can be of any suitable material which may be transparent if the exposure takes place therethrough or may be opaque. Of the transparent supports, glass, ethyl cellulose, Mylar (oriented polyethylene terephthalate) and polyolefins and similar substances are satisfactory provided they withstand the operational temperatures required and are relatively free from plasticizers which tend to diffuse into the coating layer of vehicle and sensitizer. Cellulose acetate supports which, generally speaking, are undesirable because they contain ditfusable plasticizers, can be used if a suitable barrier layer is interposed between such a support and the layer thereon.

Opaque supports are preferably flexible such as paper or synthetic sheet material. These supports can be of any color, but for certain purposes black supports are particularly suitable. The vesicles or bubbles appear white on such black supports so that a positive image is produceddirectly. When transparent supports areused, the vesicular photographs can be used as negatives since the light-exposed areas are opaque to transmitted light only.

Any solvent for the acrylonitrile copolymer may be used which is compatible with the sensitizer, as discussed in greater detail in the aforesaid U.S. patent. Acetonitrile is particularly useful. When the solutions are formed, they are coated on a backing in accordance with conventional coating techniques. The solvent is then removed by evaporation and the films are ready'for use. After exposure to light in a camera or other suitable device, the films are developed by heating to an elevated temperature, preferably in the range of 225300 F. The time of exposure will generally vary inversely with the temperature, but will usually be in the range of l-10 seconds.

The following example illustrates the preparation of a vesicular record material and its use.

Example III 3 /2 grams of the dried copolymer produced in Example I was added with stirring to 25 m1. of acetonitrile. Gentle heating was necessary to dissolve the last portion. The resulting vesicular solution was allowed to cool to room temperature. Then, as stirring continued, 4 ml. of methyl alcohol containing 0.314 gram of p-dimethyl amino diazonium zinc chloride (heated slightly to complete solution) was slowly added to the acetonitrile solution. When the mixture was uniform, it was poured out onto a glass plate and spread to form a thin, uniform coating. Solvent was removed by placing in an oven at to C. for 30 minutes.

Films prepared in accordance with Example III were exposed to a mercury vapor lamp for various periods-of time and developed for 3 seconds at approximately 250 F.

Films exposed and developed in accordance with this example were subjected to accelerated aging tests in a hot oven. The thermal stability was superior to that previously observed and no loss of image density was experienced after storing at 200 F. for 24 hours.

Example IV the directions given in Example H was slowly added with stirring to 5 /2 ml. of acetonitrile. While continuing to stir the copolymer solution, 0.036 gram of para-diazo dimethyl aniline was added. After solution was complete, uniform coatings were made on Mylar. Solvent was removed from the films by drying in an oven at 110 C. for 15 minutes.

The behaviour of the films prepared by the method of this example and exposed and developed in the manner described in Example III is essentially the same as that observedv with films prepared from acrylonitrile-ethyl acrylate copolymers.

The foregoing description has included specific examples of the invention, but it will be apparent that various modifications can be made without departing from the scope of the invention as set forth in the claims.

What is claimed is:

1. A photographic material capable of furnishing a record solely in the form of a distribution pattern of radiation scattering discontinuities formed within an otherwise substantially homogeneous vehicle, said material being in the form of a dry, Water-resistant non-hygroscopic film, the continuous phase of said film being essentially a synthetic, Water-insoluble, non-hygroscopic, non-Water swelling, highly linear thermoplastic copolymer of acrylonitrile and a member of the group consisting of lower alkyl acrylates and methacrylates in which the alkyl group has from 1 to 8 carbon atoms and in which the amount of acryonitrile is between 45 and 90 molar percent, and a light decomposable solid agent substantially uniformly dispersed therein as the sole essential decomposable agent, said decomposable agent itself being non-reactive to said vehicle and upon exposure to light decomposing into products which are chemically non-reactive to said vehicle and which solely upon warming are volatile to form said radiation scattering discontinuities only in the light struck areas in said polymer to thereby furnish said record.

2. A photographic material as set forth in claim 1 in which said copolymer is a copolymer of acryonitrile with an alkyl acrylate containing 1 to 4 carbon atoms in the alkyl group, in which the amount of acrylonitrile is 65-85 molar percent.

3. A photographic material as set forth in claim 2 in which the alkyl acrylate is ethyl acrylate.

4. A photographic material as set forth in claim 3 in which said copolymer is a copolymer of about 75% acrylonitrile and 25% ethyl acrylate.

5. A method of preparing vesicular images comprising exposing to light a photographic material capable of furnishing a record solely in the form of a distribution pattern of radiation scattering discontinuities formed within an otherwise substantially homogeneous vehicle, said material being in the form of a dry, water-resistant non-hygroscopic film, the continuous phase of said film being essentially a synthetic, water-insoluble, non-hygroscopic, non-water swelling, highly linear thermoplastic copolymer of acrylonitrile and a member of the group consisting of alkyl acrylates and methacrylates in which the alkyl group has from 1 to 8 carbon atoms and in which the amount of acrylonitrile is between and 90 molar percent, and a light decomposable solid agent substantially uniformly dispersed therein as the sole essential decomposable agent, said decomposable agent itself being nonreactive to said vehicle and upon exposure to light decomposing into products which are chemically non-reactive to said vehicle and which solely upon warming are volatile to form said radiation scattering discontinuities only in the light struck areas in said polymer to thereby furnish said record, and thereafter heating said photographic material to develop a vesicular image.

6. A method of preparing vesicular images as set forth in claim 5 in which said copolymer is a copolymer of acrylonitrile and an alkyl acrylate containing 1 to 4 carbon atoms in the alkyl group in which the amount of acrylonitrile is to 85 molar percent.

7. A method of preparing vesicular images as set forth inclaim 6 in which said acrylate is ethyl acrylate.

8. A method of preparing vesicular images as set forth in claim 7 in which said copolymer is a copolymer of about acrylonitrile and about 25% ethyl acrylate.

References Cited by the Examiner UNITED STATES PATENTS 3,032,414 5/1962 James et :al. 96-91 NORMAN G. TORCHIN, Primary Examiner. 

1. A PHOTOGRAPHIC MATRIAL CAPABLE OF FURNISHING A RECORD SOLELY IN THE FORM OF A DISTRIBUTION PATTERN OF RADIATION SCATTERING DISCONTINUITIES FORMED WITHIN AN OTHERWISE SUBSTANTIALLY HOMOGENEOUS VEHICLE, SAID MATERIAL BEING IN THE FORM OF A DRY, WATER-RESISTANT NON-HYDROSCOPIC FILM, THE CONTINUOUS PHASE OF SID FILM BEING ESSENTIALLY A SYNTHETIC, WATER-INSOLUBLE, NON-HYDROSCOPIC, NON-WATER SWELLING, HIGHLY LINEAR THERMOPLASTIC COPOLYMER OF ACRYLONITRILE AND A MEMBER OF THE GROUP CONSISTING OF LOWER ALKYL ACRYLATES AND METHACRYLATES IN WHICH THE ALKYL GROUP HAS FROM 1 TO 8 CARBON ATOMS AND IN WHICH THE AMOUNT OF ACRYONITRILE IS BETWEEN 45 AND 90 MOLAR PERCENT, AND A LIGHT DECOMPOSABLE SOLID AGENT SUBSTANTIALLY UNIFORMLY DISPERSED THEREIN AS THE SOLE ESSENTIAL DECOMPOSABLE AGENT, SAID DECOMPOSABLE AGENT ITSELF BEING NON-REACTIVE TO SAID VEHICLE AND UPON EXPOSURE TO LIGHT DECOMPOSING INTO PRODUCTS WHICH ARE CHEMICALLY NON-REACTIVE TO SAID VEHICLE AND WHICH SOLELY UPON WARMING ARE VOLATILE TO FORM SAID RADIATION SCATTERING DISCONTINUTIES ONLY IN THE LIGHT STRUCK AREAS IN SAID POLYMER TO THEREBY FURNISH SAID RECORD.
 5. A METHOD OF PREPARING VESICULAR IMAGES COMPRISING EXPOSING TO LIGHT A PHOTOGRAPHIC MATERIAL CAPABLE OF FURNISHING A RECORD SOLELY IN THE FORM OF A DISTRIBUTION PATTERN OF RADIATION SCATTERING DISCONTINUITIES FORMED WITHIN AN OTHERWISE SUBSTANTIALLY HOMOGENEOUS VEHICLE, SAID MATERIAL BEING IN THE FORM OF A DRY, WATER-RESISTANT NON-HYGROSCOPIC FILM, THE CSONTINUOUS PHASE OF SAID FILM BEING ESSENTIALLY OF SYNTHETIC, WATER-INSOLUBLE, NON-HYGROSCOPIC, NON-WATER SWELLING, HIGHLY LINEAR THERMOPLASTIC COPOLYMER OF ACRYLONITRILE AND A MEMBER OF THE GROUP CONSISTING OF ALKYL ACRYLATES AND METHACRYLATES IN WHICH THE ALKYL GROUP HAS FROM 1 TO 8 CARBON ATOMS AND IN WHICH THE AMOUNT OF ACRYLONITRILE IS BETWEEN 45 AND 90 MOLAR PERCENT, AND A LIGHT DECOMPOSABLE SOLID AGENT SUBSTANTIALLY UNIFORMLY DISPERSED THEREIN AS THE SOLE ESSENTIAL DECOMPOSABLE AGENT, SAID DECOMPOSABLE AGENT ITSELF BEING NONREACTIVE TO SAID VEHICLE AND UPON EXPOSURE TO LIGHT DECOMPOSING INTO PRODUCTS WHICH ARE CHEMICALLY NON-REACTIVE TO SAID VEHICLE AND WHICH SOLELY UPON WARMING ARE VOLATILE TO FORM SAID RADIATION SCATTERING DISCONTINUTIES ONLY IN THE LIGHT STRUCK AREAS IN SAID POLYMER TO THEREBY FURNISH SAID RECORD, AND THEREAFTER HEATING SAID PHOTOGRAPHIC MATERIAL TO DEVELOP A VESICULAR IMAGE. 